arXiv subjects

G. Lanzuisi

Publications and source records attributed to G. Lanzuisi.

At least 73 records · Page 4Linked to original sources

arXiv2017

Inferring Compton-thick AGN candidates at z>2 with Chandra using the >8 keV restframe spectral curvature

To fully understand cosmic black hole growth we need to constrain the population of heavily obscured active galactic nuclei (AGN) at the peak of cosmic black hole growth ($z\sim$1-3). Sources with obscuring column densities higher than $\mathrm{10^{24}}$ atoms $\mathrm{cm^{-2}}$, called Compton-thick (CT) AGN, can be identified by excess X-ray emission at $\sim$20-30 keV, called the "Compton hump". We apply the recently developed Spectral Curvature (SC) method to high-redshift AGN (2 5\times 10^{43}}$ erg $\mathrm{s^{-1}}$. In the Cosmological evolution survey (COSMOS), we find an observed CT fraction of $\mathrm{15^{+4}_{-3}\%}$ (40/272) or $\mathrm{32\pm11 \%}$ when corrected for the survey sensitivity. When comparing to low redshift AGN with similar X-ray luminosities, our results imply the CT AGN fraction is consistent with having no redshift evolution. Finally, we provide SC equations that can be used to find high-redshift CT AGN (z>1) for current (XMM-Newton) and future (eROSITA and ATHENA) X-ray missions.

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arXiv2017

AGN vs. host galaxy properties in the COSMOS field

The coeval AGN and galaxy evolution and the observed local relations between SMBHs and galaxy properties suggest some connection or feedback between SMBH growth and galaxy build-up. We looked for correlations between properties of X-ray detected AGN and their FIR detected host galaxies, to find quantitative evidences for this connection, highly debated in the latest years. We exploit the rich multi-wavelength data set available in the COSMOS field for a large sample (692 sources) of AGN and their hosts, in the redshift range $0.1<z<4$. We use X-ray data to select AGN and determine their properties (intrinsic luminosity and nuclear obscuration), and broad-band SED fitting to derive host galaxy properties (stellar mass $M_*$ and star formation rate SFR). We find that the AGN 2-10 keV luminosity ($L_{\rm X}$) and the host $8-1000~μm$ star formation luminosity ($L_{\rm IR}^{\rm SF}$) are significantly correlated. However, the average host $L_{\rm IR}^{\rm SF}$ has a flat distribution in bins of AGN $L_{\rm X}$, while the average AGN $L_{\rm X}$ increases in bins of host $L_{\rm IR}^{\rm SF}$, with logarithmic slope of $\sim0.7$, in the redshifts range $0.4<z<1.2$. We also discuss the comparison between the distribution of these two quantities and the predictions from hydro-dynamical simulations. Finally we find that the average column density ($N_H$) shows a positive correlation with the host $M_*$, at all redshifts, but not with the SFR (or $L_{\rm IR}^{\rm SF}$). This translates into a negative correlation with specific SFR. Our results are in agreement with the idea that BH accretion and SF rates are correlated, but occur with different variability time scales. The presence of a positive correlation between $N_H$ and host $M_*$ suggests that the X-ray $N_H$ is not entirely due to the circum-nuclear obscuring torus, but may also include a contribution from the host galaxy.

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arXiv2016

The XMM Deep Survey in the CDFS

The Chandra Deep Field South (CDF-S) was observed by XMM-Newton for a total of about 3 Ms in many periods over the past decade (2001-2002 and 2008-2009). The main goal of the survey was to obtain good quality X-ray spectroscopy of the AGN responsible for the bulk of the X-ray background. We will present the scientific highlights of the XMM-Newton survey and briefly discuss the perspectives of future observations to pursue XMM deep survey science with current and forthcoming X-ray facilities.

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arXiv2016

X-ray selection of Compton Thick AGN at high redshift

Compton Thick (CT) AGN are a key ingredient of Cosmic X-ray Background (CXB) synthesis models, but are still an elusive component of the AGN population beyond the local Universe. Multi-wavelength surveys are the only way to find them at z > 0.1, and a deep X-ray coverage is crucial in order to clearly identify them among star forming galaxies. As an example, the deep and wide COSMOS survey allowed us to select a total of 34 CT sources. This number is computed from the 64 nominal CT candidates, each counted for its N H probability distribution function. For each of these sources, rich multi-wavelength information is available, and is used to confirm their obscured nature, by comparing the expected AGN luminosity from spectral energy distribution fitting, with the absorption-corrected X-ray luminosity. While Chandra is more efficient, for a given exposure, in detecting CT candidates in current surveys (by a factor ~2), deep XMM-Newton pointings of bright sources are vital to fully characterize their properties: NH distribution above 10^25 cm^-2, reflection intensity etc., all crucial parameters of CXB models. Since luminous CT AGN at high redshift are extremely rare, the future of CT studies at high redshift will have to rely on the large area surveys currently underway, such as XMM-XXL and Stripe82, and will then require dedicated follow-up with XMM-Newton, while waiting for the advent of the ESA mission Athena.

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arXiv2016

The Chandra COSMOS Legacy Survey: Clustering of X-ray selected AGN at 2.9<z<5.5 using photometric redshift Probability Distribution Functions

We present the measurement of the projected and redshift space 2-point correlation function (2pcf) of the new catalog of Chandra COSMOS-Legacy AGN at 2.9$\leq$z$\leq$5.5 ($\langle L_{bol} \rangle \sim$10$^{46}$ erg/s) using the generalized clustering estimator based on phot-z probability distribution functions (Pdfs) in addition to any available spec-z. We model the projected 2pcf estimated using $π_{max}$ = 200 h$^{-1}$ Mpc with the 2-halo term and we derive a bias at z$\sim$3.4 equal to b = 6.6$^{+0.60}_{-0.55}$, which corresponds to a typical mass of the hosting halos of log M$_h$ = 12.83$^{+0.12}_{-0.11}$ h$^{-1}$ M$_{\odot}$. A similar bias is derived using the redshift-space 2pcf, modelled including the typical phot-z error $σ_z$ = 0.052 of our sample at z$\geq$2.9. Once we integrate the projected 2pcf up to $π_{max}$ = 200 h$^{-1}$ Mpc, the bias of XMM and \textit{Chandra} COSMOS at z=2.8 used in Allevato et al. (2014) is consistent with our results at higher redshift. The results suggest only a slight increase of the bias factor of COSMOS AGN at z$\gtrsim$3 with the typical hosting halo mass of moderate luminosity AGN almost constant with redshift and equal to logM$_h$ = 12.92$^{+0.13}_{-0.18}$ at z=2.8 and log M$_h$ = 12.83$^{+0.12}_{-0.11}$ at z$\sim$3.4, respectively. The observed redshift evolution of the bias of COSMOS AGN implies that moderate luminosity AGN still inhabit group-sized halos at z$\gtrsim$3, but slightly less massive than observed in different independent studies using X-ray AGN at z$\leq2$.

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arXiv2016

Compton Thick AGN in the 70 Month Swift-BAT All-Sky Hard X-ray Survey: a Bayesian approach

The 70-month Swift/BAT catalogue provides a sensitive view of the extragalactic X-ray sky at hard energies (>10 keV) containing about 800 Active Galactic Nuclei. We explore its content in heavily obscured, Compton-thick AGN by combining the BAT (14-195 keV) with the lower energy XRT (0.3-10 keV) data. We apply a Bayesian methodology using Markov chains to estimate the exact probability distribution of the column density for each source. We find 53 possible Compton-thick sources (with probability 3 to 100%) translating to a ~7% fraction of the AGN in our sample. We derive the first parametric luminosity function of Compton-thick AGN. The unabsorbed luminosity function can be represented by a double power-law with a break at $L_{\star} 2 \times 10^{42}$ $\rm ergs~s^{-1}$ in the 20-40 keV band.

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arXiv2016

The Chandra COSMOS-Legacy survey: Source X-ray spectral properties

We present the X-ray spectral analysis of the 1855 extragalactic sources in the Chandra COSMOS-Legacy survey catalog having more than 30 net counts in the 0.5-7 keV band. 38% of the sources are optically classified Type 1 active galactic nuclei (AGN), 60% are Type 2 AGN and 2% are passive, low-redshift galaxies. We study the distribution of AGN photon index and of the intrinsic absorption N(H,z) based on the sources optical classification: Type 1 have a slightly steeper mean photon index than Type 2 AGN, which on the other hand have average intrinsic absorption ~3 times higher than Type 1 AGN. We find that ~15% of Type 1 AGN have N(H,z)>1E22 cm^(-2), i.e., are obscured according to the X-ray spectral fitting; the vast majority of these sources have L(2-10keV)>$1E44 erg/s. The existence of these objects suggests that optical and X-ray obscuration can be caused by different phenomena, the X-ray obscuration being for example caused by dust-free material surrounding the inner part of the nuclei. ~18% of Type 2 AGN have N(H,z)<1E22 cm^(-2), and most of these sources have low X-ray luminosities (L(2-10keV)<$1E43 erg/s). We expect a part of these sources to be low-accretion, unobscured AGN lacking of broad emission lines. Finally, we also find a direct proportional trend between N(H,z) and host galaxy mass and star formation rate, although part of this trend is due to a redshift selection effect.

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arXiv2016

The Chandra COSMOS Legacy survey: the z>3 sample

We present the largest high-redshift (3 0 at z>3. We compute the number counts in the observed 0.5-2 keV band, finding a decline in the number of sources at z>3 and constraining phenomenological models of X-ray background. We compute the AGN space density at z>3 in two different luminosity bins. At higher luminosities (logL(2-10 keV) > 44.1 erg/s) the space density declines exponentially, dropping by a factor ~20 from z~3 to z~6. The observed decline is ~80% steeper at lower luminosities (43.55 erg/s < logL(2-10 keV) < 44.1 erg/s), from z~3 to z~4.5. We study the space density evolution dividing our sample in optically classified Type 1 and Type 2 AGN. At logL(2-10 keV) > 44.1 erg/s, unobscured and obscured objects may have different evolution with redshift, the obscured component being three times higher at z~5. Finally, we compare our space density with predictions of quasar activation merger models, whose calibration is based on optically luminous AGN. These models significantly overpredict the number of expected AGN at logL(2-10 keV) > 44.1 erg/s with respect to our data.

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arXiv2016

Tracing outflows in the AGN forbidden region with SINFONI

AGN driven outflows are invoked in numerical simulations to reproduce several observed properties of local galaxies. The z > 1 epoch is of particular interest as it was during this time that the volume averaged star formation and the accretion rate of black holes were maximum. Radiatively driven outflows are therefore believed to be common during this epoch. We aim to trace and characterize outflows in AGN hosts with high mass accretion rates at z > 1 using integral field spectroscopy. We obtain spatially-resolved kinematics of the [OIII]5007 line in two targets which reveal the morphology and spatial extension of the outflows. We present J and H+K band SINFONI observations of 5 AGNs at 1.2 < z < 2.2. To maximize the chance of observing radiatively driven outflows, our sample was pre-selected based on peculiar values of the Eddington ratio and the hydrogen column density of the surrounding interstellar medium. We observe high velocity (~600-1900 km/s) and kiloparsec scale extended ionized outflows in at least 3 of our targets, using [OIII]5007 line kinematics tracing the AGN narrow line region. We estimate the total mass of the outflow, the mass outflow rate, and the kinetic power of the outflows based on theoretical models and report on the uncertainties associated with them. We find mass outflow rates of ~1-10 M_sun/yr for the sample presented in this paper. Based on the high star formation rates of the host galaxies, the observed outflow kinetic power and the expected power due to the AGN, we infer that both star formation and AGN radiation could be the dominant source for the outflows. The outflow models suffer from large uncertainties, hence we call for further detailed observations for an accurate determination of the outflow properties to confirm the exact source of these outflows.

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arXiv2016

XMM-Newton reveals a Seyfert-like X-ray spectrum in the z=3.6 QSO B1422+231

Matter flows in the central regions of quasars during their active phases are probably responsible for the properties of the super-massive black holes and that of the bulges of host galaxies. To understand how this mechanism works, we need to characterize the geometry and the physical state of the accreting matter at cosmological redshifts. The few high quality X-ray spectra of distant QSO have been collected by adding sparse pointings of single objects obtained during X-ray monitoring campaigns. This could have introduced spurious spectral features due to source variability. Here we present a single epoch, high-quality X-ray spectrum of the z=3.62 quasar B1422+231 whose flux is enhanced by gravitationally lensing (F$_{2-10 keV}\sim$10$^{-12}$erg s$^{-1}$ cm$^{-2}$). The X-ray spectrum of B1422+231 is found to be very similar to the one of a typical nearby Seyfert galaxy. Neutral absorption is detected (N$_{H}\sim$5$\times$10$^{21}$ cm$^{-2}$ at the redshift of the source) while a strong absorption edge is measured at E$\sim$7.5 keV with an optical depth of $τ\sim$0.14. We also find hints of the FeK$α$ line in emission at E$\sim$6.4 keV line (EW$\lesssim$70 eV) and a hump is detected in the E$\sim$15-20 keV energy band (rest-frame) suggesting the presence of a reflection component. In this scenario, the primary emission of B1422+231 is most probably dominated by the thermal Comptonization of UV seed photons in a corona with kT$\sim$40 keV and the reflection component has a relative direct-to-reflect normalization r$\sim$1. These findings confirm that gravitational lensing is effective to obtain good quality X-ray spectral information of quasar at high-z, moreover they support the idea that the same general picture characterizing active galactic nuclei in the nearby Universe is valid also at high redshift.

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arXiv2016

X-ray observations of dust obscured galaxies in the Chandra Deep Field South

We present the properties of X-ray detected dust obscured galaxies (DOGs) in the Chandra Deep Field South. In recent years, it has been proposed that a significant percentage of the elusive Compton-thick (CT) active galactic nuclei (AGN) could be hidden among DOGs. In a previous work, we presented the properties of X-ray detected DOGs by making use of the deepest X-ray observations available at that time, the 2Ms observations of the Chandra deep fields. In that work, we only found a moderate percentage ($<$ 50%) of CT AGN among the DOGs sample, but we were limited by poor photon statistics. In this paper, we use not only a deeper 6 Ms Chandra survey of the Chandra Deep Field South (CDF-S), but combine these data with the 3 Ms XMM-Newton survey of the CDF-S. We also take advantage of the great coverage of the CDF-S region from the UV to the far-IR to fit the spectral energy distributions (SEDs) of our sources. Out of the 14 AGN composing our sample, 9 are highly absorbed (but only 3 could be CT AGN), whereas 2 look unabsorbed, and the other 3 are only moderately absorbed. In only one of the CT AGN, we detect a strong Fe K$α$ emission line; the source is already classified as a CT AGN with Chandra data in a previous work. For the other two CT candidates, the non-detection of the line could be because of the low number of counts in their X-ray spectra, but their location in the L$_{\rm 2-10\,keV}$/L$_{12μm}$ plot supports their CT classification. Although a higher number of CT sources could be hidden among the X-ray undetected DOGs, our results indicate that DOGs could be as well composed of only a fraction of CT AGN plus a number of moderate to highly absorbed AGN, as previously suggested. From our study of the X-ray undetected DOGs in the CDF-S, we estimate a percentage between 13 and 44% of CT AGN among the whole population of DOGs.

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arXiv2016

NuSTAR reveals the extreme properties of the super-Eddington accreting SMBH in PG 1247+267

PG1247+267 is one of the most luminous known quasars at $z\sim2$ and is a strongly super-Eddington accreting SMBH candidate. We obtained NuSTAR data of this intriguing source in December 2014 with the aim of studying its high-energy emission, leveraging the broad band covered by the new NuSTAR and the archival XMM-Newton data. Several measurements are in agreement with the super-Eddington scenario for PG1247+267: the soft power law ($Γ=2.3\pm0.1$); the weak ionized Fe emission line and a hint of the presence of outflowing ionized gas surrounding the SMBH. The presence of an extreme reflection component is instead at odds with the high accretion rate proposed for this quasar. This can be explained with three different scenarios; all of them are in good agreement with the existing data, but imply very different conclusions: i) a variable primary power law observed in a low state, superimposed on a reflection component echoing a past, higher flux state; ii) a power law continuum obscured by an ionized, Compton thick, partial covering absorber; and iii) a relativistic disk reflector in a lamp-post geometry, with low coronal height and high BH spin. The first model is able to explain the high reflection component in terms of variability. The second does not require any reflection to reproduce the hard emission, while a rather low high-energy cutoff of $\sim100$ keV is detected for the first time in such a high redshift source. The third model require a face-on geometry, which may affect the SMBH mass and Eddington ratio measurements. Deeper X-ray broad-band data are required in order to distinguish between these possibilities.

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arXiv2016

A fast ionised wind in a Star Forming-Quasar system at z~1.5 resolved through Adaptive Optics assisted near-infrared data

Outflows are invoked in co-evolutionary models to link the growth of SMBH and galaxies through feedback phenomena, and from the analysis of both galaxies and Active Galactic Nuclei (AGN) samples at z$\sim1-3$, it is becoming clear that powerful winds are quite common in AGN hosts. High-resolution and high S/N observations are needed in order to uncover the physical properties of the wind through kinematics analysis. We exploited VIMOS, SINFONI and Subaru/IRCS Adaptive Optics data to study the kinematics properties on the scale the host galaxy of XID5395, a luminous, X-ray obscured Starburst/Quasar merging system at z$\sim1.5$ detected in the XMM-COSMOS field, and associated with an extreme [O II] emitter (EW$\sim200$ Å). We mapped, for the first time, at high resolution the kinematics of the [O III] and H$α$ line complexes and linked them with the [O II] emission. The high spatial resolution achieved allowed us to resolve all the components of the SB-QSO system. Our analysis with a resolution of few kpc reveals complexities and asymmetries in and around the nucleus of XID5395. The velocity field measured via non parametric analysis reveals different kinematic components, with maximum blueshifted and redshifted velocities up to $\simeq1300$ km s$^{-1}$, not spatially coincident with the nuclear core. These extreme values of the observed velocities and the spatial location can be explained by the presence of fast moving material. We also spectroscopically confirm the presence of a merging system at the same redshift of the AGN host. We propose that EW as large as $>150$ Å in X-ray selected AGN may be an efficient criterion to isolate objects associated to the short, transition phase of "feedback" in the AGN-galaxy co-evolutionary path, which will subsequently evolve in an unobscured QSO, as suggested from the different observational evidences we accumulated for XID5395.

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arXiv2016

The Chandra COSMOS Legacy survey: overview and point source catalog

The COSMOS-Legacy survey is a 4.6 Ms Chandra program that has imaged 2.2 deg$^2$ of the COSMOS field with an effective exposure of $\simeq$160 ks over the central 1.5 deg$^2$ and of $\simeq$80 ks in the remaining area. The survey is the combination of 56 new observations, obtained as an X-ray Visionary Project, with the previous C-COSMOS survey. We describe the reduction and analysis of the new observations and the properties of 2273 point sources detected above a spurious probability of 2$\times 10^{-5}$. We also present the updated properties of the C-COSMOS sources detected in the new data. The whole survey includes 4016 point sources (3814, 2920 and 2440 in the full, soft and hard band). The limiting depths are 2.2 $\times$ 10$^{-16}$, 1.5 $\times$ 10$^{-15}$ and 8.9$\times$ 10$^{-16}$ ${\rm erg~cm}^{-2}~{\rm s}^{-1}$ in the 0.5-2, 2-10 and 0.5-10 keV bands, respectively. The observed fraction of obscured AGN with column density $> 10^{22}$ cm$^{-2}$ from the hardness ratio (HR) is $\sim$50$^{+17}_{-16}$%. Given the large sample, we compute source number counts in the hard and soft bands, significantly reducing the uncertainties of 5-10%. For the first time, we compute number counts for obscured (HR$>$-0.2) and unobscured (HR$<$-0.2) sources and find significant differences between the two populations in the soft band. Due to the un-precedent large exposure, COSMOS-Legacy area is 3 times larger than surveys at similar depth and its depth is 3 times fainter than surveys covering similar area. The area-flux region occupied by COSMOS-Legacy is likely to remain unsurpassed for years to come.

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arXiv2015

The Chandra COSMOS Legacy survey: optical/IR identifications

We present the catalog of optical and infrared counterparts of the Chandra COSMOS-Legacy Survey, a 4.6 Ms Chandra program on the 2.2 square degrees of the COSMOS field, combination of 56 new overlapping observations obtained in Cycle 14 with the previous C-COSMOS survey. In this Paper we report the i, K, and 3.6 micron identifications of the 2273 X-ray point sources detected in the new Cycle 14 observations. We use the likelihood ratio technique to derive the association of optical/infrared (IR) counterparts for 97% of the X-ray sources. We also update the information for the 1743 sources detected in C-COSMOS, using new K and 3.6 micron information not available when the C-COSMOS analysis was performed. The final catalog contains 4016 X-ray sources, 97% of which have an optical/IR counterpart and a photometric redshift, while 54% of the sources have a spectroscopic redshift. The full catalog, including spectroscopic and photometric redshifts and optical and X-ray properties described here in detail, is available online. We study several X-ray to optical (X/O) properties: with our large statistics we put better constraints on the X/O flux ratio locus, finding a shift towards faint optical magnitudes in both soft and hard X-ray band. We confirm the existence of a correlation between X/O and the the 2-10 keV luminosity for Type 2 sources. We extend to low luminosities the analysis of the correlation between the fraction of obscured AGN and the hard band luminosity, finding a different behavior between the optically and X-ray classified obscured fraction.

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arXiv2015

Pan-STARRS1 variability of XMM-COSMOS AGN. II. Physical correlations and power spectrum analysis

[Abbreviated] We search for scaling relations between the fundamental AGN parameters and rest-frame UV/optical variability properties for a sample of $\sim$90 X-ray selected AGNs covering a wide redshift range from the XMM-COSMOS survey, with optical light curves in four bands provided by the Pan-STARRS1 (PS1) Medium Deep Field 04 survey. To estimate the variability amplitude we utilize the normalized excess variance ($σ_{\mathrm{rms}}^{2}$) and probe variability on rest-frame timescales of several months and years by calculating $σ_{\mathrm{rms}}^{2}$ from different parts of our light curves. In addition, we derive the rest-frame optical PSD for our sources using continuous-time autoregressive moving average (CARMA) models. We observe that the excess variance and the PSD amplitude are strongly anti-correlated with wavelength, bolometric luminosity and Eddington ratio. There is no evidence for a dependency of the variability amplitude on black hole mass and redshift. These results suggest that the accretion rate is the fundamental physical quantity determining the rest-frame UV/optical variability amplitude of quasars on timescales of months and years. The optical PSD of all of our sources is consistent with a broken power law showing a characteristic bend at rest-frame timescales ranging between $\sim$100 and $\sim$300 days. The break timescale exhibits no significant correlation with any of the fundamental AGN parameters. The low frequency slope of the PSD is consistent with a value of $-1$ for most of our objects, whereas the high frequency slope is characterized by a broad distribution of values between $\sim-2$ and $\sim-4$. These findings unveil significant deviations from the simple "damped random walk" model, frequently used in previous optical variability studies. We find a weak tendency for AGNs with higher black hole mass having steeper high frequency PSD slopes.

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arXiv2015

The XMM deep survey in the CDF-S. IX. An X-ray outflow in a luminous obscured quasar at z~1.6

In active galactic nuclei (AGN)-galaxy co-evolution models, AGN winds and outflows are often invoked to explain why super-massive black holes and galaxies stop growing efficiently at a certain phase of their lives. They are commonly referred to as the leading actors of feedback processes. Evidence of ultra-fast (v>0.05c) outflows in the innermost regions of AGN has been collected in the past decade by sensitive X-ray observations for sizable samples of AGN, mostly at low redshift. Here we present ultra-deep XMM-Newton and Chandra spectral data of an obscured (Nh~2x10^{23} cm^-2), intrinsically luminous (L2-10keV~4x10^{44} erg/s) quasar (named PID352) at z~1.6 (derived from the X-ray spectral analysis) in the Chandra Deep Field-South. The source is characterized by an iron emission and absorption line complex at observed energies of E~2-3 keV. While the emission line is interpreted as being due to neutral iron (consistent with the presence of cold absorption), the absorption feature is due to highly ionized iron transitions (FeXXV, FeXXVI) with an outflowing velocity of 0.14^{+0.02}_{-0.06}c, as derived from photoionization models. The mass outflow rate - ~2 Msun/yr - is similar to the source accretion rate, and the derived mechanical energy rate is ~9.5x10^{44} erg/s, corresponding to 9% of the source bolometric luminosity. PID352 represents one of the few cases where indications of X-ray outflowing gas have been observed at high redshift thus far. This wind is powerful enough to provide feedback on the host galaxy.

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arXiv2015

SINFONI spectra of heavily obscured AGNs in COSMOS: evidence of outflows in a MIR/O target at z$\sim2.5$

We present new data for four candidate obscured Compton-Thick (CT) quasars at z $\sim$1-2.5 observed with SINFONI VLT spectrograph in AO mode. These sources were selected from a 24$μ$m Spitzer MIPS survey of the COSMOS field, on the basis of red mid-infrared-to-optical and optical-to-near-infrared colours, with the intention of identifying active galactic nuclei (AGNs) in dust enshrouded environments, where most of the black hole mass is assembled in dust enshrouded environments. Near infrared spectra were analyzed in order to check for emission line features and to search for broad components in the [OIII]-H$β$ and H$α$-[NII] regions. X-ray spectral analysis, radio and MIR diagnostics, and SED fitting have also been employed to study the nature of the sources. We successfully identified three objects for which we had only a photometric redshift estimate. Based on their emission line diagnostics and on ancillary multi-wavelength constraints, we find that all four targets harbor obscured AGNs. Broad profiles that could be attributed to the effects of outflows are revealed in only one target, MIRO20581. In particular, we clearly resolved a fast ($\sim$1600 km/s) and extended ($\sim$5 kpc) outflow in the [OIII]5007 emission line. This feature, the commonly used indicator for ionised outflowing gas, was sampled and detected only for this target; hence, we can not exclude the presence of outflows in the other sources. Overall, the constraints we obtain from our targets and from other comparative samples from the literature suggest that these optically faint luminous infrared galaxies, hosting obscured AGNs, may represent a brief evolutionary phase between the post-merger starburst and the unobscured QSO phases.

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